So you've got a SQL Server Reporting Services .rdl file and you want to open the report in Visual Studio and modify it. But it just keeps showing you the XML of the report. You've installed all the right SQL Server Data Tools / Business Intelligence Studio (BIDS) bits for your version of Visual Studio and all that jazz.
Double-clicking the file from Windows Explorer shows you an XML view, not the report designer. File -> Open also shows you XML and not the report designer. How the hell do you get the report designer view to open?
You need to have a Report Server Project (.rptproj) and add the .rdl file to that. Then, finally, Visual Studio knows that the .rdl file is a report and will open the Report Designer for you.
Ah the fun of setting up a new machine, installing lots of tools and wondering why things don't work the way they used to.